Measure once, order with confidence.
A clear, step-by-step guide to measuring your opening for every product we make. Get your sizes right and your live price will be spot on.
Four golden rules
These apply to every product. Get them right and the rest is easy.
- A steel tape measure
- A pencil and paper
- A spirit level
- A second pair of hands for wide openings
Measure the opening, not the old frame
If you're replacing a window or door, remove the old frame first. You want the masonry or structural opening size.
Measure at three points, use the smallest
Openings are rarely perfectly square. Measure width at top, middle and bottom; height at left, middle and right.
Always work in millimetres
Our configurator uses mm. Centimetres and inches introduce rounding errors — use millimetres throughout.
Check, then check again
Every product is made to your measurements. A minute re-checking your figures now avoids delays and costs later.
Measure in three places, use the smallest
-
1
Width. Measure the opening at the top, middle and bottom. Openings are rarely perfectly square.
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2
Height. Measure the left, middle and right of the opening, from the same fixed points each time.
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3
Use the smallest. Take the smallest width and smallest height. This is your structural opening size.
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4
Work in millimetres. Always record in mm and double-check every figure before you configure.
Choose your product
Each product measures a little differently. Pick yours for a tailored diagram and steps.
Measuring bifold doors
- 1
Overall width. Measure the full masonry opening from reveal to reveal at three heights. Use the smallest.
- 2
Overall height. Measure from the floor (or sill) to the underside of the lintel at three points. Use the smallest.
- 3
Panel configuration. Decide how many panels and which way they stack. Enter this in the configurator.
- 4
Sill detail. Note whether you need a sill and whether the floor is level — this affects how the door is installed.
Measuring sliding doors
- 1
Structural opening. Measure the full masonry opening width and height. Always use the smallest of three measurements.
- 2
Floor level. Check the floor is level across the full width — sliding doors run on a bottom track and need a level base.
- 3
Track options. Consider whether a raised or flush track suits your floor type and transition detail.
- 4
Slide direction. Note which way you want the panels to slide — enter this in the configurator.
Measuring entrance & French doors
- 1
Opening width. Measure across the masonry opening at three heights. Use the smallest for your order.
- 2
Opening height. Measure from the sill / floor to the underside of the lintel. Use the smallest of three points.
- 3
Handing. Note which direction the doors open (in or out) and which leaf is the master door.
- 4
Threshold. Decide on your threshold type — standard, low, or rebated — to suit your floor level and drainage.
Measuring internal doors
- 1
Structural opening. Remove the existing frame if replacing. Measure the masonry opening at three points each way.
- 2
Floor to ceiling. Internal doors are typically taller. Measure from finished floor level to underside of lintel.
- 3
Handing. Note the swing direction and the handle side. This determines the leaf orientation.
- 4
Wall thickness. Internal doors often need deeper frames — note your wall thickness before ordering.
Measuring for roof lanterns
- 1
Upstand / kerb opening. Measure the internal dimensions of the upstand the lantern will sit on — width and length.
- 2
Kerb height. Measure the height of the upstand above the roof deck — this determines the base frame height.
- 3
Square check. Measure diagonals on the upstand — they should match within 5 mm for a square fit.
- 4
Ridge orientation. Note which way the ridge runs (length or width) relative to the building.
Measuring flat rooflights
- 1
Structural / kerb opening. Measure the internal dimensions of the opening or upstand the rooflight will cover.
- 2
Upstand detail. Check the upstand height — frameless rooflights need a minimum upstand to ensure weathering.
- 3
Roof pitch. Confirm the roof is flat or confirm the pitch — our rooflights are designed for flat and very low-pitch roofs.
- 4
Access. If you need a walk-on or access rooflight, confirm this in the configurator as it affects the specification.
Common mistakes to avoid
A few minutes of care here saves a lot of hassle later.
Measuring an existing frame
Always measure the structural opening, not the old door or window frame that is in the way.
Assuming the opening is square
Walls move over time. Measuring in three places and using the smallest protects you.
Mixing up units
Work in millimetres throughout and write every figure down as you go.
Printable measuring templates
A branded A4 sheet for each product, with diagrams, measurement fields and an options checklist. Enter your email and download the one you need, or grab the full pack.
- Print at 100%, no scaling
- One sheet per product
- Fields for every measurement
We'll send a copy to your inbox. Unsubscribe any time.
Measuring responsibility
All products are made to the measurements you provide, so responsibility for the accuracy of those measurements rests with you. SmartaView is a supply-only business and does not provide a measuring, surveying or installation service. Please follow this guide carefully and measure more than once. If you are at all unsure, we recommend appointing a suitably qualified professional to take or check your measurements before you order. We cannot accept responsibility, or offer a refund or replacement, for products that do not fit because the measurements supplied were incorrect. This does not affect your statutory rights in respect of faulty or misdescribed goods.
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